There is a need for a fast predominantly solid phase process for forming articles directly from powdered thermoplastic resin materials. Such powder formed parts can be made at a lesser expense than a comparable part made by either an injection molding technique or a conventional vacuum forming process. The reasons for the favorable economics of powder formed parts are elimination of a pelletizing step, absence of excess scrap, a reduced cooling cycle and a more efficient material utilization.
Further, a process having relatively short heat cycle times is especially desired when fabricating thermally unstable resinous powders, such as the crystalline vinylidene halide polymers.
More particularly, the present invention is directed to a specific powder-forming process whereby decomposition-free, substantially fused, flexible plastic articles are unexpectedly obtained by utilization of certain processing conditions while employing resinous powders of specified morphology, i.e., resinous powders having a "lamellar crystalline nonspherulitic" morphology. The use of such materials would not be obvious to the skilled worker as these materials are generally of relatively low-bulk density and are subsequently difficult to handle. Further, that such results were unexpected is illustrated by the comparative data set forth in Example III herein wherein resins employed in their more conventional nonlamellar crystalline morphology were incapable of being forged into clear, void-free, flexible articles. Still further, the capability of the present process to provide decomposition-free, substantially clear, flexbile articles was unexpected in view of the teaching of U.S. Pat. No. 3,502,639 which requires the use of annealed "oriented" crystalline structures wherein the lamellae are stacked parallel to one another. Such teaching clearly leads away from the present invention wherein substantially "unoriented" briquettes are forged into shaped articles.